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The Painful Psychological Cost Of Becoming A Dad - Darby Saxbe - #1129
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The Real Cause of Dad Brain
At 18:25 · chapter starts 17:56
The central mechanism of dad brain is one of the episode's most striking insights: biology requires behaviour. Mothers arrive at birth with their caregiving dial already turned all the way up — incubating a pregnancy costs thousands of calories and hard-wires the investment. Fathers' dials sit in the middle by default, available to rise or fall based on local demands. Saxbe introduces the concept of facultative adaptation to describe this: a biological capacity that only comes online when activated by the environment. [1] — Darby Saxbe "Mother's caregiving drive is turned all the way up at birth — incubating a pregnancy costs thousands of calories and locks in that investme…" 18:06 She draws on paternity uncertainty as an evolutionary explanation for fathers' more conditional attachment — uniquely among primates, humans conceal ovulation, incentivising men to pair bond and invest across multiple visits rather than helicopter in for a single encounter. The stability of the relationship with the mother, Saxbe adds, further modulates a father's predilection to caregive.
Mother's caregiving drive is turned all the way up at birth — incubating a pregnancy costs thousands of calories and locks in that investment. Fathers' dial sits in the middle by default, ready to rise or fall based on culture, relationship stability, and hands-on practice. This is facultative adaptation: biology that comes online when needed.
The Westermarck effect shows that witnessing parental care of an infant between ages 1 and 10 hard-wires a sexual aversion to that person. It explains the failure of sim pua marriages in parts of Asia — and by analogy, why paternal bonding is built through caregiving behavior rather than genetic fact.
